In the semiconductor industry mounting apparatus or sample holders (so called chucks) are used as handling apparatus for supporting and fixing flat semiconductor substrates, especially wafers. The wafers lie flat, when supported by the mounting apparatus, and are fixed and can be transported to various handling steps and processing stations.
Typically, it is necessary to transfer the wafer from one mounting apparatus to another. Not only is reliable and flat support/fixing necessary, but detachment of the wafer as simply and carefully as possible, also plays a major part.
The fixing takes place for example by applying a vacuum between the wafer and the mounting apparatus, by electrostatic charging or by other controllable chemical-physical adhesion properties. The detachment of the wafer becomes technically more and more difficult due to the increasingly thinner wafer, which is sometimes even polished on both sides, and the optionally existing inherent adhesion of the wafer to the sample holder. The surfaces on which fixing takes place can also be provided with a pattern, grooving or any other topography which further reduces the contact surface in order to obtain a mounting surface as small as possible.
Avoiding contamination is also an important aspect.
The latter is important in methods and devices for bonding of two substrates (wafers), especially in the critical step of contact-making of the aligned contact surfaces of the two opposite substrates, where the requirement is for more and more exact alignment accuracy or offset of less than 2 μm, especially less than 250 nm, preferably less than 150 nm, more preferably less than 50 nm. To attain these alignment accuracies, many influencing factors must be considered. But the deposition/contact-making of the substrates is especially critical since faults can occur here, and the faults can add up and thus a reproducible alignment accuracy cannot be maintained. This leads to considerable scrap.
The object of this invention is therefore to provide a device and a method for bonding of two substrates, mainly for prebonding or temporary bonding, wherein alignment accuracy as good as possible is achieved everywhere on the wafer, and wherein contamination of the substrate is avoided.
Hereinafter the words “bonding, temporary bonding and prebonding” will be used synonymously. It is clear to one skilled in the art that the invention was developed preferably, but not in a limiting manner, in order to join two wafers to one another by a prebond, as much as possible in a blanketing manner, free of distortions and strain.
For prebonding to produce a temporary or reversible bond between the substrates, there are several methods which are known to one skilled in the art. The prebond thicknesses are below the permanent bond thicknesses, at least by the factor of 2 to 3, especially by the factor 5, preferably by the factor 15, still more preferably by the factor 25. Guideline values are prebond thicknesses of pure, nonactivated, hydrophilized silicon with roughly 100 mJ/m2 and of pure, plasma-activated, hydrophilized silicon with roughly 200-300 mJ/m2. The prebonds between the molecule-wetted substrates arise mainly due to the van-der-Waals interactions between the molecules of the different sides of the wafers.
Bonding means for bonding and/or prebonding and/or temporary bonding are intended for bonding as claimed in the invention.
This object is achieved with the features of the independent Claims. Advantageous developments of the invention are given in the dependent claims. All combinations of at least two of the features given in the specification, the claims and/or the figures also fall within the framework of the invention. At the given value ranges values which lie within the indicated limits are also to be considered disclosed and claimed in any combination.